Process for the electrolytic production of manganese dioxide with frequent replacement of smooth anodes



United States Patent poration of Germany No Drawing. Filed Nov. 17, 1966, Ser. No. 594,979

Claims priority, application Germany, Nov. 30, 1965,

Int. 01. con, i5/04, 13/14 US. Cl. 204-83 14 Claims The present invention relates to a process for the electrolytic production of manganese dioxide, wherein a manganous salt, particularly manganous sulfate, dissolved in a sulfuric acid solution, is subjected to anodic oxidation with the use of lead or lead-alloy anodes.

The electrolytic production of manganese dioxide generally comprises subjecting an acid manganese salt solution to electrolytic treatment. The electrolysis is known to be carried out with the use of graphite or coal anodes, or metal anodes, particularly lead or lead-alloy or titanium anodes, or metal oxide anodes.

The use of lead or lead-alloy anodes in the electrolytic production of manganese dioxide is beset with disadvantages. Manganese dioxide produced in conventional manner and removed from the anodes after two or more periods of electrolysis is found always to be more or less contaminated with lead (chiefly in the form of PbO PbSO lead manganite or in metallic form). The contamination is the result of the steadyily increasing roughness of the anode surface area, caused by corrosion, and it impairs the storability of dry cells, wherein manganese dioxide is the depolarization mass.

Manganese dioxide produced eltctrolytically has now unexpectedly been found to contain lead in a proportion increasing from period to period of electrolysis, provided that the very same anodes are used for making it. This disadvantage can be substantially obviated by replacement of the anodes after single or three times repeated use thereof, preferably after single use of the anodes in the electrolysis, which is carried out over a period of 7 to 40 days, preferably over a period of to 30 days, with fresh anodes.

The electrodes to replace the used electrodes are preferably made by remelting the used anodes and subsequently compressing or casting the molten lead alloy. Care should be taken to ensure that the anode surface has a mean roughness of less than 50g, preferably of less than 20 To this end, anodes are successfully used which are formed of either a lead alloy with a content of antimony between 1 and 15% by weight, preferably between 2 and 7% by weight, and with a content of tellurium between 0 and 0.15% by weight, preferably between 0.03 and 0.10% by weight, with the balance lead, or are formed of a lead alloy with a content of antimony between 2 and 8% by weight, preferably between 3 and 6% by weight, and with a content of tin between 0 and 6% by weight, preferably between 1 and 4% by weight, with the balance lead.

Anodes having a smooth surface, which is so desirable,

3,455,798 Patented July 15, 1969 are obtained by pouring the lead melt into a crucible mold having very smooth, preferably polished inside surfaces, the crucible being first maintained at a temperature above the melting point of the lead alloy. The melt is thereafter allowed to solidify inside the crucible by gradually cooling it from below to above. This means that during solidification of the melt, it is tightly pressed under its own weight against the wall of the crucible. Castings so made have a surface considerably smoother than that of normal lead castings. Neatly trimmed, preferably polished extrusion dies should be used for extrusion of the lead melt into tubular structures. The electrolytes used include solutions containing 1 to 20% by weight, preferably 5 to 10% by weight sulfuric acid, and 2 to 10% by weight, preferably 3 to 6% by weight manganese in the form of 'manganous sulfate. These solutions are then subjected to electrolysis at a temperature between and 100 C., preferably between and 98 C., at a current density between 0.5 and 1.5, preferably between 0.7 and 1.3 amperes per square decimeter.

For example, extruded lead alloy pipes may have a mean roughness of about 5 determined in the longitudinal direction of the grooves, for a height of the grooves of about 20a. When used as the anodes in the electrolytic production of manganese dioxide under conventional conditions to be freed after 7 to 40 days, often after 10 to 30 days, from the electrolytic manganese dioxide grown fast thereto, they are found to have a mean roughness say of 60 determined in the longitudinal direction of the grooves. The lead content of the manganese dioxide is then often less than 0.10% weight. However, when the anodes are used once again for carrying out the electrolysis under identical conditions, the lead content of the manganese dioxide generally increases to a value of about 0.10 to 0.20% by weight and more. The mean roughness, determined in the longitudinal direction of the anodes, is then found to be, for example 90 or more. When the same anodes are used a third time for carrying out the electrolysis under identical conditions, the lead content of the manganese dioxide then increases generally to a value considerably higher than 0.1% by weight, often to a value between 0.2 and 0.7% by weight.

The same applies to lead alloy anodes cast under the above conditions, where the initial surface roughness of about 4,11, determined in the longitudinal direction of the anodes, is found to increase say to 50g after a period of electrolysis of about 10 to 30 days under conventional conditions, the lead content of the manganese dioxide being less than 0.10% by weight. When used once again for electrolysis under identical conditions, they produce manganese dioxide containing about 0.10 to 0.20% by weight lead and more. The anode surface is then found to have a mean roughness of about 807.4. or more. When anodes having such a surface structure are used a third time for electrolysis under identical conditions, the lead content in the manganese dioxide is found to be considerably higher than 0.1% by weight, and it is often found to be 0.2 to 0.6% by weight.

In other words, greater roughness of the lead alloy anodes always results in an increased lead content of the electrolytic manganese dioxide produced with these anodes, as clearly demonstrated in the working examples compiled in the following Tables la, lb, 1c.

TABLE 1a .-II 6Sb+3 Sn 1 Determined in the longitudinal direction of the anodes.

TABLE 1b Height of grooves Mean roughness 1 (I4) Pb-content MnOz wt. percent 1st period of electrolysis (d ys) Mean Lead alloy with roughnesal Anode type wt. percent- Extruded 4 Sb Do 3 Sb Do Sb+0.05 Te--.. Cast 6 Sb+3 Sn K Determined in the longitudinal direction of the anodes.

TABLE Mean Lead alloy with roughnescsu wt. percent- Anode type 1 Determined in the longitudinal direction of the anodes.

We claim:

1. In the process for the electrolytic production of manganese dioxide by subjecting a manganous salt dissolved in a sulfuric acid solution to anodic oxidation with the use of lead-alloy anodes, the improvement which comprises replacing the anodes, after single to threetimes repeated use thereof in an electrolysis carried out over a period of 7 to 40 days, with fresh anodes.

2. The process of claim 1, wherein the anodes are replaced after single use thereof in an electrolysis carried out over a period of 10 to 30 days, with fresh anodes.

3. The process of claim 1, wherein the anodes to replace the used anodes are made by remelting the used anodes and subsequently compressing the lead alloy.

4. The process of claim 1, wherein the anodes to replace the used anodes are made by remelting the used anodes and subsequently casting the lead alloy.

. 5. The process of claim 1, wherein the anodes have a surface with a mean roughness of less than 50 6. The process of claim 5, wherein the anode surface has a mean roughness of less than 20 7. The process of claim 1, wherein the anodes are formed of a lead alloy with a content of antimony between 1 and by weight and with a content of tellurium between 0 and 0.15% by weight, thebalance being lead.

8. The process of claim 7, wherein the anodes are formed of a lead alloy with a content of antimony between 2 and 7% by weight and with a content of tellurium between 0.03 and 0.10% by Weight, the balance being lead.

9. The process of claim 1, wherein the anodes are formed of a lead alloy with a content of antimony between 2 and 8% by weight and with a content of tin between 0 and 6% by weight, the balance being lead.

10. The process of claim 9, wherein the anodes are formed of a lead alloy with a content of antimony between 3 and 6% by weight and with a content of tin between 1 and 4% by weight, the balance being lead.

11. The process of claim 4, wherein the lead melt is Height of grooves (11) Height of grooves (u) Pb-content of MnO-z wt. percent Mean 2nd period of roughness 1 (u) electrolysis (d ys) Pb-content of MnO wt. percent Mean 3rd period of roughness 1 (M) electrolysis (d y poured into a crucible mold having very smooth inside surfaces, the crucible mold being first maintained at a temperature above the melting point of the lead alloy, and the melt is subsequently allowed to solidify inside the crucible mold by allowing it gradually to cool from below to above.

12. The process of claim 4, wherein the lead alloy is extruded into pipes using neatly trimmed extrusion dies.

13. The process of claim 1, wherein a solution containing 1 to 20% by Weight sulfuric acid and 2 to 10% by weight manganese in the form of manganous sulfate is electrolyzed at a temperature between and 100 C. and at a current density between 0.5 and 1.5 amperes per square decimeter.

14. The process of claim 13, wherein a solution containing 5 to 10% by weight of sulfuric acid and 3 to 6% by weight manganese in the form of manganous sulfate is electrolyzed at a temperature between and 98 C. and at a current density between 0.7 and 1.3 amperes per square decimeter.

References Cited UNITED STATES PATENTS 8/1947 Clemens 20483 US. Cl. X.R. 

1. IN THE PROCESS FOR THE ELECTROLYTIC PRODUCTION OF MANGANESE DIOXIDE BY SUBJECTING A MANGANOUS SALT DISSOLVED IN A SULFURIC ACID SOLUTION TO ANODIC OXIDATION WITH THE USE OF LEAD-ALLOY ANODES, THE IMPROVEMENT WHICH COMPRISES REPLACING THE ANODES, AFTER SINGLE TO THREETIMES REPEATED USE THEREOF IN AN ELECTROLYSIS CARRIED OUT OVER A PERIOD OF 7 TO 40 DAYS, WITH FRESH ANODES. 